Storage medium location detection system and program

ABSTRACT

A storage medium-compatible communications unit, a phase detection unit, a parameter acquisition section and a location detection section are provided. The storage medium-compatible communications unit communicates with a storage medium by wireless using electromagnetic waves at a predetermined frequency. The phase detection unit detects phases of signals received from the storage medium. The parameter acquisition section acquires a distance detection parameter to be used in detecting a storage medium distance from a first position of an antenna to the storage medium. The first position is a position in a range of positions of the antenna from which the distance to the storage medium is shortest. The distance detection parameter is a value set in accordance with a positional relationship between the first position and a second position. The second position is a position of the antenna in the range of positions of the antenna that is different from the first position. The location detection section detects the storage medium distance, using a first phase detected by the phase detection unit at the first position, a second phase detected by the phase detection unit at the second position, and the distance detection parameter acquired by the parameter acquisition section. The location detection section identifies the first position at a time at which a trend of changes of phase detected by the phase detection unit in association with movement of the antenna reverses.

TECHNICAL FIELD

The present invention relates to a storage medium location detectionsystem and program. This application claims priority from JapanesePatent Application No. 2015-216099, filed Oct. 16, 2015, the disclosureof which is incorporated by reference herein.

BACKGROUND ART

A technology is known that, with a view to detecting the location of aradio frequency identification (RFID) tag, utilizes phases of plural tagsignals that are obtained in accordance with a user moving an RFIDtag-compatible reader and determines a bearing on which the RFID tag isdisposed (for example, see Patent Document 1).

However, in the technology described above, although the bearing onwhich the RFID tag is disposed can be detected, a distance to the RFIDtag is not detected. A technology is known (for example, see PatentDocument 2) that detects a distance to an RFID tag as described below. Areader transmits plural signals to an RFID tag using plural signals withdifferent fundamental frequencies. In response to these signaltransmissions, the RFID tag applies backscatter modulation to the pluralsignals. The reader determines phases of the pluralbackscatter-modulated signals received from the RFID tag, and determinesa rate of change of the phases of the backscatter modulation signalswith respect to a rate of change of the fundamental frequencies of thetransmitted signals. The reader then utilizes information on thedetermined rate of change of phase to calculate the distance to the RFIDtag.

Patent Document 1: European Patent Application, Publication No. 2779020

Patent Document 2: U.S. Pat. No. 7,119,738

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in the technology recited in Patent Document 2, in order toobtain high accuracy in detection of distances, sufficient frequencydifferences between the plural signals that are transmitted and receivedbetween the reader and the RFID tag must be assured. On the other hand,the range of frequencies assigned for communications with an RFID tag islimited. As a result, in practice it is difficult to assure sufficientfrequency differences between the plural signals transmitted andreceived between the reader and the RFID tag, and it is difficult toimprove distance detection accuracy. A further technique is known fordetecting distance on the basis of the strengths of signals that areader receives from an RFID tag. However, distances detected by thistechnique may not be considered to be accurate enough.

The present invention has been made in consideration of thecircumstances described above and an object of the present invention isto provide a storage medium location detection system and program thatmay detect a distance to a storage medium with high accuracy.

Means for Solving the Problems

One aspect of the present invention for solving the problem describedabove is a storage medium location detection system including: a storagemedium-compatible communications unit that communicates with a storagemedium by wireless using electromagnetic waves at a predeterminedfrequency; a phase detection unit that detects phases of signalsreceived from the storage medium; a parameter acquisition section thatacquires a distance detection parameter to be used in detecting astorage medium distance from a first position of an antenna to thestorage medium, the first position being a position in a range ofpositions of the antenna from which the distance to the storage mediumis shortest, the distance detection parameter being a predeterminedvalue set in accordance with a positional relationship between the firstposition and a second position, and the second position being a positionof the antenna in the range of positions of the antenna that isdifferent from the first position;

and a location detection section that detects the storage mediumdistance, the location detection section using a first phase detected bythe phase detection unit at the first position, a second phase detectedby the phase detection unit at the second position, and the distancedetection parameter acquired by the parameter acquisition section,wherein the location detection section identifies the first position ata time at which a trend of changes of phase detected by the phasedetection unit in association with movement of the antenna reverses.

Effects of the Invention

As described above, according to the present invention, an effect isprovided in that a storage medium location detection system and programthat may detect a distance to a storage medium with high accuracy may beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of the exterior of a taglocation detection system according to a present embodiment.

FIG. 2 is a diagram depicting an example of a method for detection ofthe location of an RFID tag according to the present embodiment.

FIG. 3 is a diagram illustrating an example of changes with the passageof time of phases detected by a tag reader according to the presentembodiment.

FIG. 4 is a diagram depicting an alternative example of a method fordetection of the location of an RFID tag according to the presentembodiment.

FIG. 5 is a diagram illustrating an example of a mode of a tag locationindication screen according to the present embodiment.

FIG. 6A, FIG. 6B and FIG. 6C are diagrams illustrating an example ofdisplay progress of a horizontal direction tag location indication imageaccording to the present embodiment.

FIG. 7 is a diagram illustrating an example of configuration of the tagreader and a portable terminal device according to the presentembodiment.

FIG. 8 is a flowchart illustrating a processing sequence example that isexecuted by the portable terminal device according to the presentembodiment in order to detect a tag location and output a display of thedetected tag location.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Below, a storage medium location detection system according to anembodiment of the present invention is described with reference to theattached drawings. The storage medium that is the object of locationdetection in the present embodiment is a radio frequency identification(RFID) tag. In the following descriptions, the RFID tag may be referredto simply as “the tag”.

FIG. 1 shows an example of the exterior of the tag location detectionsystem according to the present embodiment. The tag location detectionsystem in FIG. 1 is equipped with a tag reader 100 and a portableterminal device 200. The tag reader 100 communicates by wireless with anRFID tag 300 using electromagnetic waves. In the present embodiment, thetag reader 100 and RFID tag 300 communicate using a predeterminedfrequency range in the ultra-high frequency (UHF) band. Note, however,that a frequency range that the tag reader 100 and RFID tag 300 use tocommunicate in the present embodiment is not particularly limited. Thetag reader 100 is equipped with a grip portion 111 and an antenna 101that is provided at a distal end portion of the grip portion 111. Thedirection indicated by arrow Y in FIG. 1 is, for example, a direction inwhich directionality of the antenna 101 is strongest (below referred toas “the antenna orientation direction”). When a user is using the tagreader 100, the user should hold the grip portion 111 in one hand andpoint the antenna 101 toward the RFID tag 300 that is an object ofcommunication.

The portable terminal device 200 utilizes information on phases ofsignals that the tag reader 100 receives from the RFID tag 300 to detectthe location of the RFID tag 300 (a tag location). In the presentembodiment, the portable terminal device 200 may detect a distance tothe RFID tag and a bearing of the RFID tag to serve as the tag location.To output the detected tag location, the portable terminal device 200displays a tag location screen representing the tag location on adisplay unit 205.

The portable terminal device 200 is fixed to the tag reader 100 by anadapter ADP. In the state in which the portable terminal device 200 isfixed by the adapter ADP, the portable terminal device 200 is disposedsuch that a screen of the display unit 205 faces toward the user holdingthe tag reader 100. Therefore, the user may see the screen of theportable terminal device 200 fixed to the tag reader 100 at all timeswhile holding the tag reader 100. The portable terminal device 200according to the present embodiment may be a dedicated terminal or maybe, for example, a general-purpose terminal such as a smartphone or thelike on which an application is installed that performs functionsrelating to tag location detection and display of a detected taglocation.

The RFID tag 300 according to the present embodiment is used in, forexample, administration of products displayed in a store. The RFID tags300 are mounted to each of the products displayed in the store. Forexample, when a product is being sold, a tag reader at a register mayconduct price processing and sale results administration by retrievinginformation in product codes (for example, a JAN code, a price and thelike) stored in the RFID tag mounted at the product that a customerwishes to buy. In this environment, there may be cases in which aspecific product should be sought out among the products displayed inthe store. In this situation, if the location of the tag mounted to thatproduct can be identified, the product being sought can be found quicklyand precisely without reliance on the memory of a store employee or thelike. It is desirable if the accuracy of the detected location is ashigh as possible. Accordingly, in the present embodiment, the taglocation detection system including the tag reader 100 and portableterminal device 200 as illustrated in FIG. 1 is configured so as todetect a tag location with high accuracy. A configuration for thispurpose is described below.

When a tag location is being detected with the tag location detectionsystem according to the present embodiment, a user holds the tag reader100 to which the portable terminal device 200 is fixed, points the tagreader 100 in a direction in which the RFID tag 300 being sought islikely to be located, and moves the tag reader 100 so as to swing theantenna orientation direction represented by arrow Y in FIG. 1 in anarbitrary direction up or down and left or right. This movement of thetag reader 100 may be resolved into a movement component in a horizontaldirection H and a movement component in a vertical direction V, whichare shown in FIG. 1. If the tag reader 100 communicates with the RFIDtag 300 being sought in accordance with the state in which the tagreader 100 is being moved as described above, the tag location isdetected by the portable terminal device 200 and the detected locationis displayed on the display unit 205 of the portable terminal device200.

Referring to FIG. 2, an example of a method for detection of the taglocation in the present embodiment is described. A case in which theantenna 101 of the tag reader 100 is moved in a straight line in ahorizontal direction during tag location detection is given as anexample. In FIG. 2, position P_(tag) represents a position of the RFIDtag 300 in a horizontal direction (a plan view direction). A position P₀and a position P₁ are respective, mutually different positions of theantenna 101 (antenna positions) that are attained during the linearmovement of the tag reader 100 in the horizontal direction. A case inwhich position P₁ corresponds to the start of the movement of the tagreader 100 and position P₀ is attained at a later time in the movementof the tag reader 100 is given as an example. In this case, position P₀is the antenna position in the movement path of the antenna 101 at whichthe distance from the antenna 101 to the RFID tag 300 is shortest.

As illustrated in FIG. 2, a triangle is formed by position P_(tag),position P₀ and position P₁. In the triangle whose vertices are atposition P_(tag), position P₀ and position P₁, the angle of the vertexat position P₀ is 90°. Thus, the triangle formed by the vertices atposition P_(tag), position P₀ and position P₁ is a right-angledtriangle.

A round-trip distance 2D₀ between position P_(tag) and position P₀ shownin FIG. 2 is expressed by the following Equation 1.

$\begin{matrix}{{2\; D_{0}} = {{n\; \lambda} + \frac{\lambda \; \Phi_{0}}{2\; \pi}}} & \left( {{Formula}\mspace{14mu} 1} \right)\end{matrix}$

In Equation 1, the symbol λ represents the wavelength of a carrier waveof a first frequency that is transmitted and received between the tagreader 100 and the RFID tag 300. The symbol n represents a number ofcycles of the carrier wave. The symbol Φ₀ represents a phase of signalsreceived from the RFID tag 300 at position P₀, which phase is detectedby the tag reader 100.

A round-trip distance 2D₁ between position P_(tag) and position P₁ isexpressed by the following Equation 2.

$\begin{matrix}{{2\; D_{1}} = {{n\; \lambda} + \frac{\lambda \; \Phi_{0}}{2\; \pi} + \frac{\lambda \; \Delta \; \Phi}{2\; \pi}}} & \left( {{Formula}\mspace{14mu} 2} \right)\end{matrix}$

A phase of signals received from the RFID tag 300 at position P₁ that isdetected by the tag reader 100 is φ₁. In Equation 2, the symbol ΔΦrepresents a difference (a phase difference) between the phases Φ₁ andΦ₀. The phase difference ΔΦ is expressed by the following Equation 3.

ΔΦ=Φ₁−Φ₀  (Formula 3)

Because the triangle whose vertices are at position P_(tag), position P₀and position P₁ is a right-angled triangle, the tag distance D₀, thedistance D₁ and a distance b satisfy the relationship in the followingEquation 4.

D ₀ ² +b ² =D ₁ ²  (Formula 4)

Therefore, based on Equation 1, Equation 2 and Equation 4, the tagdistance D₀ can be expressed by the following Equation 5. The tagdistance D₀ is the distance to the RFID tag 300 that the tag locationdetection system according to the present embodiment is intended todetect as the location of the RFID tag 300.

$\begin{matrix}{D_{0} = {{\frac{2\; \pi}{\lambda \; \Delta \; \Phi}b^{2}} - \frac{\lambda \; \Delta \; \Phi}{8\pi}}} & \left( {{Formula}\mspace{14mu} 5} \right)\end{matrix}$

The tag distance D₀ can be calculated from Equation 5 even if ΔΦ isgreater than 2π. Therefore, there is no limitation on the length of thedistance b in a calculation of the tag distance D₀ according to Equation5.

In Equation 5, the wavelength λ is already known. Therefore, in order tocalculate the tag distance D₀ from the antenna 101 to the RFID tag 300,it is necessary to acquire the phase difference ΔΦ and the distance b.

As shown by Equation 3, the phase difference ΔΦ in Equation 5 is thedifference between phase Φ₀ and phase Φ₁. Therefore, to acquire thephase difference ΔΦ, it is sufficient to acquire the phase P₀ detectedat position P₀ and the phase Φ₁ detected at position P₁. The presentembodiment is configured to be capable of detecting the phases ofsignals that the tag reader 100 receives from the RFID tag. To find thetag distance D₀ with Equation 5, it is also necessary to identify theposition P₀, at which the distance to the RFID tag 300 is shortest, in amovement range (position range) of the antenna 101 when the movement ofthe antenna 101 has started from position P₁.

A number of modes for acquisition of the distance b can be considered.Here, two representative examples of modes of acquisition of thedistance b are mentioned. In one mode, a value of a movement speed ofthe tag reader 100 (a reader movement speed) v for calculating thedistance b, which is a value fixed beforehand, is stored in the portableterminal device 200 in advance. When a tag distance D₀ is beingcalculated with Equation 5, the distance b is calculated by multiplyinga movement duration t by the stored reader movement speed v. When a userholds the tag reader 100 in their hand and moves the tag reader 100 inorder to detect a tag location, the movement speed of the antenna 101 isgenerally consistent. Therefore, a single value may be set as the readermovement speed v on the basis of a general movement speed of the antenna101 when the tag reader 100 is held by hand and moved, and this valuemay be stored in the portable terminal device 200 in advance. In theother mode, the portable terminal device 200 is equipped with anacceleration sensor. The portable terminal device 200 uses detectionoutputs from the acceleration sensor to calculate the distance movedfrom position P₁ to position P₀ in a movement of the tag reader 100. Forexample, speeds during the movement from position P₁ to position P₀ arecalculated on the basis of detection outputs from the accelerationsensor. Hence, the movement distance from position P₁ to position P₀ canbe calculated from durations and speeds taken in the movement fromposition P₁ to position P₀. The portable terminal device 200 may acquirethis calculated movement distance to serve as the distance b.

In the present embodiment, position P₀ may be identified by the portableterminal device 200 as follows. FIG. 3 shows an example of changes withthe passage of time of phases of a tag disposed at P_(tag) (1 m) thatare detected by the tag reader 100, in a case in which the tag reader100 is moved a distance b (1.25 m) in the horizontal direction fromposition P₁. The horizontal axis in FIG. 3 represents time and thevertical axis represents phase angle. In this case, in a period ofmovement lasting approximately 1.25 s, from −3.0 s when the movement ofthe antenna 101 is started to around −1.75 s, the distance from theantenna 101 to the RFID tag 300 is longer than the shortest distancethereof, and the phase repeatedly changes through a negative trend inthe range from 2π to 0. The phase difference ΔΦ from −3.0 s toapproximately −1.75 s is about 7π. Subsequently, when the antenna 101 ismoved further and the distance to the RFID tag 300 departs from theminimum distance, the phase reverses from the falling trend to a risingtrend at time t0. That is, a phenomenon occurs in which the trend ofchanges of phase (more specifically, the trend of trend linescorresponding to changes in phase with the passage of time) is reversed.This phenomenon is caused by the antenna 101 moving toward the RFID tag300 and the tag distance D₀ decreasing up to time t0, and then thedistance D₀ increasing after time t0, as can be understood from Equation1 above. Thus, the position of the antenna 101 at time t0 when thisphenomenon occurs corresponds to position P₀ shown in FIG. 2.Thereafter, as the antenna 101 continues to move in the same direction,the antenna 101 moves away from the RFID tag 300 again, during which thephase repeatedly changes through a positive trend in the range from 0 to2π. Accordingly, the portable terminal device 200 monitors the phases ofreceived signals detected by the tag reader 100 in accordance with amovement of the antenna 101, and determines a time at which the trend ofchanges of phase reverses. Position P₀ can be identified by thedetermination of this time.

From the above description, it can be seen that changes in phase followa negative trend in a state in which a movement direction of the antenna101 is toward the RFID tag 300 and changes in phase follow a positivetrend in a state in which a movement direction of the antenna 101 isaway from the RFID tag 300. Thus, it is possible to identify from atrend of changes of phase with the passage of time whether the antenna101 and the RFID tag 303 are moving closer together or moving apart.

Because there are multiple electromagnetic wave paths between theantenna 101 and the RFID tag 300, waves may overlap (multipaths). As aresult, locations at which data cannot be retrieved from the RFID tag300 (null points) may occur and there may be temporary vibrations inphase data (noise may be generated). However, many values of the phasedifference ΔΦ may be acquired in the process of movement of the antenna101, and multipath effects in an ordinary indoor environment may beeliminated by calculating the trend lines using the least squares methodor the like.

Position P₀ is identified, at which the distance from the antenna 101 tothe RFID tag 300 is a shortest distance within the movement range of theantenna 101, indicating that the antenna orientation directionrepresented by arrow Y in FIG. 1 is pointing directly toward the RFIDtag 300. That is, the bearing on which the RFID tag 300 is disposed maybe identified by identifying position P₀. Accordingly, the portableterminal device 200 is provided with a sensor (a magnetic sensor, anacceleration sensor, an angular velocity sensor or the like) thatdetects directions (azimuth angles and elevation angles). The portableterminal device 200 acquires the direction that this sensor detects atthe time t0 at which position P₀ is identified. Thus, the portableterminal device 200 may detect the bearing on which the RFID tag 300 isdisposed in the horizontal direction (the plan view direction).

The portable terminal device 200 according to the present embodimentfurther identifies a position P₀ in the vertical direction in accordancewith a movement of the antenna 101 of the tag reader 100 in the verticaldirection (a side view direction) by the same method as the methoddescribed with FIG. 2 and FIG. 3. Thus, the portable terminal device 200according to the present embodiment may both find the bearing anddistance of a tag location in the horizontal direction and find abearing and distance of the tag location in the vertical direction.

In the present embodiment, with the detection method described above,the tag distance may be detected with high accuracy in association withboth a horizontal bearing and a vertical bearing even though signalsbased on a single frequency are being transmitted and received betweenthe tag reader 100 and the RFID tag 300. In the process of calculatingthe distance, the bearing on which the RFID tag 300 is disposed may alsobe detected with high accuracy. That is, in the present embodiment, atag location may be detected with high accuracy within the range of afrequency band assigned to communications between the RFID tag 300 andthe tag reader 100.

The actual location of the RFID tag 300 by reference to the antenna 101is located in a three-dimensional space. Therefore, it is difficult toprecisely identify the bearing of the RFID tag 300 according to theactual location of the RFID tag 300 within the three-dimensional spacefrom only one of detection results for the bearing of the RFID tag 300in the horizontal direction and detection results for the bearing of theRFID tag 300 in the vertical direction. Correspondingly, it is difficultto appropriately indicate the actual location of the RFID tag 300 in thethree-dimensional space from only one of detection results for thedistance of the RFID tag 300 in the horizontal direction and detectionresults for the distance of the RFID tag 300 in the vertical direction.

Therefore, in the present embodiment the tag location located in thethree-dimensional space is identified by combining the detection resultsof the tag location in the horizontal direction with the detectionresults of the tag location in the vertical direction. To be specific,in the process of movement of the antenna 101, the portable terminaldevice 200 detects the bearing of the RFID tag 300 from a direction in aplane in which a position P₀ is identified first, which is thehorizontal direction or the vertical direction. Then, at a time at whicha position P₀ is identified for a direction in the other plane, which isorthogonal to the one plane in which the bearing of the RFID tag 300 wasdetected first, the portal terminal 200 detects the distance and bearingfrom the direction in the other plane. The distance and bearing that areultimately detected in this manner accurately express the distance andbearing according to the actual location of the RFID tag 300 in thethree-dimensional space.

Now, an alternative example of a method for detection of the taglocation according to the present embodiment is described with referenceto FIG. 4. First, a case in which the tag location (distance andbearing) is detected in the horizontal direction is described. In theabove example of a method for detection of the tag location according toFIG. 2, the movement of the antenna 101 is simplified to a straightline. However, when a user is detecting a tag location, a movement pathof the antenna 101 when the tag reader 100 is held in a user's hand andmoved in order to seek the location of the RFID tag 300 may beconsidered to form, for example, a circular arc centered on the user'selbow.

If the movement path of the antenna 101 is treated as forming a circulararc centered on the elbow of the user as described above, then as shownin FIG. 4, position P₀ and position P₁ of the horizontal direction arepositions on a line of circumference with a center O, corresponding tothe location of the elbow, and a radius r, corresponding to a forearmlength from the elbow. As shown in FIG. 4, a line from position P₁ whichis orthogonal to a radius line r linking position P₀ with the center Ois denoted “c”, an end point of line c at the radius line r linkingposition P₀ with center O is denoted “A”, and a line from position P₀ topoint A is denoted “a”. A central angle formed between the radius thatpasses through position P₀ on the circumference and a radius that passesthrough position P₁ on the circumference (that is, a central angle whenposition P₀ and position P₁ are the two ends of an arc) is denoted “0”.In this situation, the length of line c is expressed by the followingEquation 6.

c=r·sin θ  (Formula 6)

Hence, the tag distance D₀ and distance D₁ satisfy the relationshipexpressed by the following Equation 7.

(D ₀ +a)²+(r sin θ)² =D ₁ ²  (Formula 7)

The length of line a may be expressed by the following Equation 8.

a=r−r·cos θ=r(1−cos θ)  (Formula 8)

Therefore, after the phase difference ΔΦ is found, the tag distance D₀in the horizontal direction can be calculated by the following Equation9 based on Equation 7 and Equation 8.

$\begin{matrix}{D_{0} = \frac{{- {ar}} + {\frac{1}{2}\left( \frac{\lambda \; \Delta \; \Phi}{4\; \pi} \right)^{2}}}{a - \frac{\lambda \; \Delta \; \Phi}{4\; \pi}}} & \left( {{Formula}\mspace{14mu} 9} \right)\end{matrix}$

A method for identifying the position P₀ in the case of the example inFIG. 4 may be similar to the method described with FIG. 3. Accordingly,in the case of the example in FIG. 4, the direction detected by thesensor at the time at which position P₀ is identified on the basis ofchanges of phase is acquired, and the acquired direction may be used asa detection result for the bearing of the RFID tag 300 in the horizontaldirection.

According to Equation 9, the tag distance D₀ can be found if values ofthe radius r and central angle θ are acquired. As mentioned above, theradius r corresponds to the forearm length of the user holding the tagreader 100. Although the forearm lengths of users differ betweendifferent users, the forearm lengths of humans fall within a certainrange; individual differences are in a range from a few cm to 10 cm orso. Therefore, a value may be fixed for the radius r on the basis of anaverage human forearm length and stored in advance in the portableterminal device 200. Hence, in a calculation of the tag distance D₀based on Equation 9, it is sufficient for the portable terminal device200 to acquire the stored value of the radius r. Alternatively, theforearm length of the user operating the tag reader 100 may be measuredand the measured length value may be stored in the portable terminaldevice 200 by user operations to be the radius r.

In order to acquire the central angle θ, for example, a direction sensordevice is provided in the portable terminal device 200. In associationwith a movement of the antenna 101 in the horizontal direction, adifference is calculated between an angle detected by this sensor deviceat the time at which the movement in the horizontal direction startsfrom position P₁ and an angle detected by the sensor device at the timeat which position P₀ is identified. The portable terminal device 200 mayacquire the difference that is found in this manner to be the centralangle θ.

As described above, the portable terminal device 200 may acquire theradius r and a central angle θ corresponding to a movement of theantenna 101 in the horizontal direction and use Equation 9 to calculatethe tag distance D₀ for the horizontal direction. Similarly, theportable terminal device 200 may acquire the radius r and a centralangle θ corresponding to a movement of the antenna 101 in the verticaldirection and use Equation 9 to calculate the tag distance D₀ for thevertical direction. In this case too, a bearing of the RFID tag 300located in a three-dimensional space may be detected with high accuracyby combining detection results of the bearing of the RFID tag 300 in thehorizontal direction with detection results of the bearing of the RFIDtag 300 in the vertical direction. Furthermore, the tag distance locatedin the three-dimensional space may be detected with high accuracy bycalculating the distance in accordance with the bearing that is detectedin this manner.

The portable terminal device 200 outputs the tag location detected asdescribed above in a display. FIG. 5 illustrates an example of a mode ofa tag location indication screen that is displayed at the display unit205 of the portable terminal device 200. The tag location indicationscreen is a screen that shows a detected location of the RFID tag 300.

A tag name area AR1 is disposed in the tag location indication screen ofFIG. 5. In the tag name area AR1, information corresponding to a name ofthe RFID tag 300 that is the target of location detection is displayed.FIG. 5 shows an example in which a serial number assigned to the tag isdisplayed in the tag name area AR1.

A horizontal direction tag location indication image Gh and a verticaldirection tag location indication image Gv are disposed in the taglocation indication screen. The horizontal direction tag locationindication image Gh is an image showing a tag location detected in thehorizontal direction. The vertical direction tag location indicationimage Gv is an image showing a tag location detected in the verticaldirection.

In the horizontal direction tag location indication image Gh, a circularplan view over 360° corresponding to the horizontal direction (plan viewdirection) is disposed to serve as a background. Thereon, an antennaobject OBJ1 representing the antenna 101 of the tag reader 100 isdisposed at the center of the circular plan view. The antenna objectOBJ1 turns at the center of the circular plan view so as to show thecurrent antenna orientation direction in the horizontal direction. Asearch range image ZNh in a fan shape is superposed on the circular planview of the horizontal direction tag location indication image Gh. Thesearch range image ZNh represents an angular range through which theantenna orientation direction of the antenna 101 has been moved in thehorizontal direction for tag location detection by the tag reader 100. Atag object OBJ2 is disposed on the circular plan view of the horizontaldirection tag location indication image Gh. The tag object OBJ2 is animage disposed on the circular plan view so as to indicate a taglocation detected in the horizontal direction.

FIG. 6A to FIG. 6C illustrate an example of progress from when a userstarts movement of the tag reader 100 (that is, movement of the antenna101) until the horizontal direction tag location indication image Gh isshown in FIG. 5. Before the user starts the movement of the tag reader100, first, the user holds the tag reader 100 in a stationary state fora certain duration (for example, around 5 s). When the portable terminaldevice 200 detects this state in which the tag reader 100 is stationaryfor the certain duration, the portable terminal device 200 sets thestate at this time as an initial state. In the initial state, thehorizontal direction tag location indication image Gh is displayed inthe mode illustrated in FIG. 6A. That is, the antenna object OBJ isdisplayed on the horizontal direction tag location indication image Ghin a state of being oriented directly upward, which is a referencedirection. In other words, the angle to which the antenna orientationdirection is oriented that is detected in the initial state is set asthe reference direction.

Now, an example is described in which the user starts a movement of thetag reader 100 so as to turn the antenna orientation direction leftwardabout their elbow from the initial state described above. In associationwith this movement of the tag reader 100, as shown in FIG. 6B, theantenna object OBJ changes direction so as to turn in thecounterclockwise direction from the state of being oriented directlyupward. As the antenna object OBJ1 turns as described above and thedirection thereof is changed, the search range image ZNh is changed soas to expand in the counterclockwise direction from the referencedirection. As depicted in FIG. 3, the phase of signals being receivedchanges in accordance with the movement of the tag reader 100, that is,the movement of the antenna 101. The trend of changes of phase isidentified as being positive or negative. On the basis of the trend ofchanges of phase, it is determined whether the movement direction of theantenna 101 is toward the location of the RFID tag 300 or away from thelocation of the RFID tag 300. On the basis of this determination result,a tag direction indication image Arr is also displayed on the horizontaldirection tag location indication image Gh, in an arrow shape indicatinga direction to the RFID tag 300. FIG. 6B shows an example in which thecurrent movement of the antenna 101 is toward the RFID tag 300.Therefore, the tag direction indication image Arr is displayed pointingin the same direction as the direction in which the antenna object OBJ1is turning. By observing this display, the user can understand that theRFID tag 300 is located at the direction in which the tag reader 100 iscurrently being moved. On the other hand, if the movement of the tagreader 100 is started so as to turn the antenna orientation directionrightward, opposite to the example in FIG. 6B, the trend of changes ofphase is positive and it is determined that the antenna 101 is movingaway from the RFID tag 300. In this case, the antenna object OBJ1 isdisplayed so as to turn in the clockwise direction, but the tagdirection indication arrow Arr is displayed so as to point in thecounterclockwise direction, opposite to the direction of turning of theantenna object OBJ1. By observing this display, the user can understandthat the direction in which the tag reader 100 is currently being movedis not the direction toward where the RFID tag 300 is located.

In the process of the tag reader 100 being moved such that the antennaorientation direction turns further in the counterclockwise directionfrom FIG. 6B, a reversal of the trend of changes of phase occurs at acertain time. This is a state in which the antenna orientation directionin the horizontal direction corresponds with the location of the RFIDtag 300 (a state in the movement path of the antenna 101 in thehorizontal direction in which the distance between the RFID tag 300 andthe antenna 101 is shortest). Accordingly, the portable terminal device200 detects the location (distance and bearing) in the horizontaldirection as described above. Then, in accordance with the detectedbearing and distance, the portable terminal device 200 displays the tagobject OBJ2 on the circular plan view as illustrated in FIG. 6C. If, forexample, the antenna orientation direction is subsequently turnedfurther leftward, the display progresses as shown in FIG. 6C. That is,the antenna object tag object OBJ2 continues to be displayed at the sameposition on the circular plan view, while the antenna object OBJ1 turnsfurther in the counterclockwise direction in accordance with themovement of the antenna orientation direction, and the search rangeimage ZNh expands further in the counterclockwise direction. If the userthen changes the direction of movement of the antenna 101 to theclockwise direction from the direction of the antenna object OBJ1 shownin FIG. 6C, the antenna object OBJ1 also turns in the clockwisedirection, tracking the direction of movement of the antenna 101.However, the search range image ZNh stays in the state shown in FIG. 6Crather than tracking the movement of the antenna 101 in the clockwisedirection. That is, the search range image ZNh shows the maximum rangethat has been searched from the start of the movement of the antenna 101to the present moment.

Description now returns to FIG. 5. In the vertical direction taglocation indication image Gv, a semicircular plan view over 180°corresponding to the vertical direction (side view direction) isdisposed to serve as the background. Thereon, an antenna object OBJ11representing the antenna 101 of the tag reader 100 is disposed at thecenter of the semicircle of the semicircular plan view. The antennaobject OBJ11 turns at the center of the semicircle of the semicircularplan view so as to show the current angle of the antenna orientationdirection in the vertical direction. A search range image ZNv in a fanshape is superposed on the semicircular plan view of the verticaldirection tag location indication image Gv. The search range image ZNvrepresents an angular range through which the antenna orientationdirection of the antenna 101 has been moved in the vertical directionfor tag location detection. A tag object OBJ12 is disposed on thesemicircular plan view of the vertical direction tag location indicationimage Gv. The tag object OBJ12 is an image disposed on the semicircularplan view so as to indicate a tag location detected in the verticaldirection.

The vertical direction tag location indication image Gv is displayed ina procedure corresponding to the description of FIG. 6A to FIG. 6C. Thatis, an up-down angle detected when movement is started serves as areference direction in the vertical direction. In accordance withmovement of the antenna 101 in the vertical direction, the antennaobject OBJ11 turns on the semicircular plan view, the search range imageZNv expands, and a tag direction indication image Arr is displayed. Whena state in which the antenna orientation direction corresponds with thetag location is reached (a state in the movement path of the antenna 101in the vertical direction in which the distance between the RFID tag 300and the antenna 101 is shortest), the portable terminal device 200detects the location (distance and bearing) of the RFID tag 300 in thevertical direction. Then, in accordance with the detected bearing anddistance, the portable terminal device 200 disposes the tag object OBJ12on the semicircular plan view.

A distance indication area AR2 is also disposed in the tag locationindication screen. The distance indication area AR2 is an area thatrepresents the current tag distance with a numerical value.

By observing the horizontal direction tag location indication image Ghand the vertical direction tag location indication image Gv in the taglocation indication screen, the user may instinctively and accuratelyunderstand the location (bearing and distance) of the RFID tag 300 in athree-dimensional space. Furthermore, because a specific numerical valueis displayed in the distance indication area AR2, the user may moreprecisely understand the distance of the location of the RFID tag 300 inthe three-dimensional space. Subsequently, the user walks toward theRFID tag 300 and the phase changes. The distance D₀ decreases by adistance amount that is found by dividing a phase change amount by 2πand multiplying by the wavelength λ. Accordingly, the numerical value ofdistance displayed in the distance indication area AR2 may be displayedso as to decrease in accordance with movement of the user.

FIG. 7 illustrates an example of configuration of the tag reader 100 andportable terminal device 200 according to the present embodiment. First,structures of the tag reader 100 are described with reference to FIG. 7.The tag reader 100 is equipped with the antenna 101, a tag-compatiblecommunications unit 102, a phase detection unit 103 and a portableterminal device-compatible communications unit 104. The antenna 101transmits and receives electromagnetic waves to and from the RFID tag300 (FIG. 1). The tag-compatible communications unit 102 communicateswith the RFID tag 300 by wireless using electromagnetic waves with apredetermined wavelength. As mentioned above, the tag-compatiblecommunications unit 102 according to the present embodiment maycommunicate using a predetermined wavelength in the UHF band. The phasedetection unit 103 detects the phases of signals received from the RFIDtag 300. The portable terminal device-compatible communications unit 104communicates with the portable terminal device 200. A communicationssystem of the portable terminal device-compatible communications unit104 with the portable terminal device 200 is not particularly limited,but the following examples may be mentioned. If communicating by wire,the portable terminal device-compatible communications unit 104 maycommunicate by, for example, USB (Universal Serial Bus (registeredtrademark)), a wired local area network (LAN) or the like. Ifcommunicating by wireless, the portable terminal device-compatiblecommunications unit 104 may communicate by Bluetooth (registeredtrademark), a wireless LAN or the like. With regard to ease of handlingfor users, wireless communication is preferable. In the presentembodiment, the portable terminal device-compatible communications unit104 transmits phase information representing phases detected by thephase detection unit 103 to the portable terminal device 200.

Now, structures of the portable terminal device 200 are described withreference to FIG. 7. The portable terminal device 200 is equipped with atag reader-compatible communications unit 201, a sensor unit 202, acontrol unit 203, a memory unit 204, the display unit 205, and anoperation unit 206. The tag reader-compatible communications unit 201communicates with the tag reader 100. The communication system of thetag reader-compatible communications unit 201 corresponds with thecommunication system of the portable terminal device-compatiblecommunications unit 104. The sensor unit 202 is a section containing oneor more sensors to be used in tag location detection. Corresponding withthe descriptions above, the sensor unit 202 can include a magnetismsensor, an acceleration sensor, an angular acceleration sensor andsuchlike.

The control unit 203 performs control relating to tag location detectionand outputs of detection results at the portable terminal device 200.Functions of the control unit 203 are realized by a CPU (centralprocessing unit) provided at the portable terminal device 200 executinga program. The control unit 203 provides functional sections of aparameter acquisition section 231, a location detection section 232 andan output section 233.

As a distance detection parameter to be used in detecting the tagdistance Do (an example of a storage medium distance) from position P₀to the RFID tag 300, the parameter acquisition section 231 acquires apredetermined value set in accordance with a positional relationshipbetween position P₀ (an example of a first position) and position P₁ (anexample of a second position) that is a different position of theantenna. In the case of the method described with FIG. 2, the distancedetection parameter is a reader movement speed v to be used incalculating the distance b between position P₀ and position P₁. Theparameter acquisition section 231 may acquire a value of the distance bthat is stored in the memory unit 204 as a fixed value, as mentionedabove. Alternatively, the parameter acquisition section 231 maycalculate a movement amount from position P₁ to position P₀ on the basisof detection outputs of an acceleration sensor provided at the sensorunit 202 and acquire the calculated movement amount to serve as thedistance b. In the case of the method described with FIG. 4, thedistance detection parameter is the radius r of the circumference onwhich position P₀ and position P₁ are disposed. In this case, theparameter acquisition section 231 may acquire a predetermined valuestored in the memory unit 204 as the radius r, which is a fixed value oris set in accordance with the length from the elbow of the user, asdescribed above. The parameter acquisition section 231 may calculate thecentral angle θ using angles of position P₁ and position P₀ that aredetected by a direction sensor provided at the sensor unit 202, asdescribed above.

The location detection section 232 detects the storage medium distance(the tag distance D₀) using a phase Φ₀ detected by the phase detectionunit 103 at position P₀ (an example of a first phase), a phase Φ₁detected by the phase detection unit 103 at position P₁ (an example of asecond phase), and the distance detection parameter acquired by theparameter acquisition section 231. That is, in the case of the methoddescribed with FIG. 2, the location detection section 232 calculates thetag distance D₀ from Equation 5, using the value of the distance b thatis acquired to be the distance detection parameter by the parameteracquisition section 231. In the case of the method described with FIG.4, the location detection section 232 calculates the tag distance D₀from Equation 9, using the values of the central angle θ and the radiusr that are acquired to be distance detection parameters by the parameteracquisition section 231.

As described with FIG. 3, the location detection section 232 detects thedirection of the antenna 101 that is detected at the time at whichposition P₀ is identified as the bearing measured from position P₀ onwhich the RFID tag 300 is disposed (the storage medium bearing).

The output section 233 outputs the distance of the RFID tag 300 andbearing of the RFID tag 300 that have been calculated by the locationdetection section 232 in a display. That is, the output section 233displays, for example, the tag location identification screen inaccordance with the mode illustrated in FIG. 5 to FIG. 6C using thedistance and bearing of the RFID tag 300 acquired by the locationdetection section 232.

The memory unit 204 stores various kinds of information to be used bythe control unit 203. As described above, the memory unit 204 may storea tag movement speed v, radius r or the like set as a constant to be adistance detection parameter.

The display unit 205 is a section that displays images in accordancewith control by the control unit 203. The operation unit 206 displaysoperation elements (keys, buttons and the like) integrally with an inputdevice (for example, a touch panel or the like) with which the portableterminal device 200 is equipped. The control unit 203 executes processesin accordance with operations performed on the operation elements, inputdevice and the like included in the operation unit 206.

Now, an example of a processing sequence that the portable terminaldevice 200 according to the present embodiment executes in order todetect a tag location and output a display of the detected tag locationis described with reference to the flowchart in FIG. 8. The control unit203 of the portable terminal device 200 waits (“NO” in step S101) untila time at which detection of a tag location is to be started. Asdescribed above, when a user starts detection of a tag location, theuser holds the tag reader 100 to which the portable terminal device 200is fixed in their hand, as illustrated in FIG. 1, and keeps the tagreader 100 in a stationary state for a predetermined duration (forexample, around 5 s). When the portable terminal device 200 determinesthat the stationary state has continued for the predetermined duration,for example, on the basis of detection outputs from an accelerationsensor provided at the sensor unit 202, the portable terminal device 200determines that this is a time to start detection of a tag location(“YES” in step S101).

In response to the time to start detection of the tag location, theoutput section 233 shows an initial display of the tag locationindication screen (step S102). In the initial state of the tag locationindication screen, the antenna object OBJ1 is disposed on the horizontaldirection tag location indication image Gh in the state of beingoriented directly upward, which is the reference direction. The searchrange image ZNh is not yet displayed; the tag object OBJ2 is also notyet displayed. Similarly, in the initial state of the tag locationindication screen, the antenna object OBJ11 is disposed on the verticaldirection tag location indication image Gv in a state of being orientedhorizontally (straight across), which is the reference direction. Thesearch range image ZNv is not yet displayed; the tag object OBJ12 isalso not yet displayed. No meaningful value representing distance isdisplayed in the distance indication area AR2.

In addition, in response to the time to start detection of the taglocation, the parameter acquisition section 231 of the control unit 203initializes settings of parameters to be used in the tag locationdetection and the display of the tag location indication screen (stepS103). More specifically, in step S103 the parameter acquisition section231 initializes parameters of an initial antenna direction(initial_direction), an antenna direction difference (direction_diff), amaximum antenna direction difference (direction_diff_max), and a phaseand direction history (list_phase_time). The initial antenna directionis a parameter representing the antenna direction in the initial state.The initial antenna direction includes an antenna horizontal angle andan antenna vertical angle. The initial antenna direction is expressed,for example, as follows.

intial_direction=[Azimuth],[Pitch]

The horizontal angle and vertical angle of the antenna direction at thetime of starting location detection are assigned to the antennahorizontal angle ([Azimuth]) and the antenna vertical angle ([Pitch]),respectively. The horizontal angle and vertical angle of the antennadirection may be, for example, calculated by the parameter acquisitionsection 231 using a direction indicated by a sensor provided at thesensor unit 202.

The antenna direction difference is a parameter representing differencesbetween a current antenna horizontal angle and antenna vertical angleand the initial antenna direction. Respective values of the antennahorizontal angle and antenna vertical angle in the antenna directiondifference are assigned initial values of 0. Thus, the initial value ofthe antenna direction difference is expressed, for example, as follows.

direction_diff=[0,0]

An antenna direction difference range is a parameter representing rangesof differences in the antenna horizontal angle and the antenna verticalangle that have been detected from the start of location detection to apresent time. The range is expressed by two angle differences, minimumand maximum, relative to the angle represented by the initial antennadirection. Therefore, the antenna direction difference range includestwo angle values representing a range corresponding to antennahorizontal angles and two angle values representing a rangecorresponding to antenna vertical angles. In the initial state, allangle values of the antenna direction difference range are 0. Thus, theinitial value of the antenna direction difference range is expressed,for example, as follows.

direction_diff_max=[0,0,0,0]

The phase and direction history is a parameter representing phases andantenna directions detected from the start of location detection to acurrent time. The phase and direction history represents phases (phase)and antenna directions (antenna horizontal angle (Azimuth) and antennavertical angle (Pitch)) detected at respective times (time). In theinitial state, no meaningful values have been acquired for any of thetime, phase and antenna direction. Thus, the initial value of the phaseand direction history is expressed, for example, as follows.

list_phase_time<time,phase,Azimuth,Pitch>=null

After the initial display of the tag location indication screen (stepS102) and the initial setting of the parameters (step S103) as describedabove, for example, a processing loop is executed at a constant timeinterval until tag location detection is completed, to detect the taglocation and display the tag location indication screen in order topresent detection results. In the loop processing, first, the parameteracquisition section 231 acquires a phase for a current time (step S104).The tag reader 100 sends phase information representing the phasedetected by the phase detection unit 103. As the processing of stepS104, the parameter acquisition section 231 acquires a phase representedby the phase information received from the tag reader 100. The parameteracquisition section 231 also acquires the antenna direction at thecurrent time (step S105). The parameter acquisition section 231 inputsthe horizontal angle and vertical angle detected by the sensor unit 202at the current time. The parameter acquisition section 231 uses theinputted horizontal angle to calculate the antenna horizontal angle, anduses the inputted vertical angle to calculate the antenna verticalangle. Thus, the parameter acquisition section 231 acquires the antennadirection by calculating the antenna horizontal angle and the antennavertical angle.

Then, the parameter acquisition section 231 uses the antenna directionacquired in step S105 and the initial antenna direction set in step S103to update the antenna direction difference parameter (step S106).

The parameter acquisition section 231 also uses the antenna directionacquired in step S105 and the initial antenna direction set in step S103to update the antenna direction difference range parameter (step S107).If either of the antenna horizontal angle and the antenna vertical angleas the antenna directions acquired in step S105 is within the precedingantenna direction difference range, there is no need to update theantenna direction difference range in step S107.

The parameter acquisition section 231 updates the phase and directionhistory parameter (step S108). This processing to update the phase anddirection history appends the phase acquired in the most recent stepS104 and the antenna direction acquired in step S105 to the phase anddirection history in association with the current time.

Then, the output section 233 makes a determination as to whether theantenna direction difference updated in step S106 exceeds apre-specified threshold (step S109). The determination in step S109 isapplied to the difference value of each of the antenna horizontal angleand the antenna vertical angle of the antenna direction difference. Thethreshold may be set in consideration of the smallest angle that can bevisually discerned in changes of direction of the antenna objects OBJ1and OBJ11 and in changes in display of the search range images. Thethreshold may also be set in consideration of the smallest angleprovided in the history of phases that can identify whether the antenna101 is moving toward or away from the RFID tag 300 according to a usualmovement speed of the antenna 101. In specific terms, a value of around,for example, 10% of the angular range can be considered for thethreshold. For the antenna horizontal angle, because the angular rangeis 360°, the threshold may be set to, for example, 36°. For the antennavertical angle, because the angular range is 180°, the threshold may beset to, for example, 18°.

If the difference in either of the antenna horizontal angle of theantenna direction difference and the antenna vertical angle of theantenna direction difference exceeds the threshold, (“YES” in stepS109), the output section 233 updates the orientation of the antennaobject OBJ1 or OBJ11 in the tag location indication screen (step S110)on the basis of the antenna direction difference updated in step S106.The output section 233 updates the orientation of antenna object OBJ1 onthe basis of the difference in the antenna horizontal angle representedby the antenna direction difference. The output section 233 also updatesthe orientation of antenna object OBJ11 on the basis of the differencein the antenna vertical angle represented by the antenna directiondifference.

On the basis of the antenna direction difference range updated in stepS107, the output section 233 displays one or both of the search rangeimage ZNh and the search range image ZNv (step S111). That is, if thedifference in the antenna horizontal angle of the antenna directiondifference has been determined to exceed the threshold in step S109, thesearch range image ZNh is displayed in step S111 so as to show the rangeaccording to the two difference values in the antenna horizontal angleof the antenna direction difference range. If the difference in theantenna vertical angle of the antenna direction difference has beendetermined to exceed the threshold in step S109, the search range imageZNv is displayed in step S111 so as to show the range according to thetwo difference values in the antenna vertical angle of the antennadirection difference range.

The output section 233 also displays the tag direction indication imagesArr (step S112). If the difference in the antenna horizontal angle ofthe antenna direction difference has been determined to exceed thethreshold in step S109, in step S112 the output section 233 displays thetag direction indication image Arr on the horizontal direction taglocation indication image Gh. When the tag direction indication imageArr is to be displayed on the horizontal direction tag locationindication image Gh, the output section 233 identifies the movementdirection of the antenna 101 in the horizontal direction on the basis ofthe history of the antenna horizontal angle represented in the phase anddirection history updated in step S108. The output section 233 makes adetermination as to whether the current movement direction of theantenna 101 corresponds to movement toward or away from the RFID tag 300by identifying whether the trend according to changes in phaserepresented in the phase and direction history updated in step S108 ispositive or negative. If it is determined that the movement is towardthe RFID tag 300, the output section 234 displays the tag directionindication image Arr on the horizontal direction tag location indicationimage Gh so as to point in the same direction as the identified movementdirection of the antenna 101. On the other hand, if it is determinedthat the movement is away from the RFID tag 300, the output section 234displays the tag direction indication image Arr on the horizontaldirection tag location indication image Gh so as to point in theopposite direction to the current movement direction of the antenna 101.If the difference in the antenna vertical angle of the antenna directiondifference has been determined to exceed the threshold in thedetermination of step S109, in step S112 the output section 233 displaysthe tag direction indication image Arr on the vertical direction taglocation indication image Gv in a similar manner.

If neither the antenna horizontal angle difference nor the antennavertical angle difference of the antenna direction difference exceedsthe threshold (“NO” in step S109), the processing of steps S110 to S112is skipped.

Next, the location detection section 232 refers to the history of phasesin the phase and direction history and makes a determination as towhether a bearing identification point has been reached (step S113).This bearing identification point is the point in time at which thetrend of changes of phase reverses in association with the minimum inthe distance from the antenna 101 to the RFID tag 300, as illustrated bytime t0 in FIG. 3.

If the bearing identification point has been reached (“YES” in stepS113), the location detection section 232 identifies (detects) thebearing (tag bearing) of the RFID tag 300 (step S114). The locationdetection section 232 acquires the antenna direction at the time of thebearing identification point reached in step S113 from the phase anddirection history. This acquired antenna direction is, in other words,the tag bearing. The location detection section 232 makes a furtherdetermination as to whether the tag bearing identified at this timecorresponds to the horizontal direction or the vertical direction. Thelocation detection section 232 refers to the phase and direction historyand, for example, compares a change amount in the antenna horizontalangle with a change amount in the antenna vertical angle over a certainduration before and after the bearing identification point. If theresult of the comparison is that the change amount in the antennahorizontal angle is larger, the identified tag bearing corresponds tothe horizontal direction, and if the result of the comparison is thatthe change amount in the antenna vertical angle is larger, theidentified tag bearing corresponds to the vertical direction.

The position of the antenna 101 at the time at which the bearing of theRFID tag 300 is identified in step S114 corresponds to position P₀ shownin FIG. 2 or FIG. 4. That is, position P₀ is identified in associationwith the bearing of the RFID tag 300 identified in step S114. If thebearing of the RFID tag 300 in the horizontal direction is identified bystep S114, position P₀ in the horizontal direction is identified, and ifthe bearing of the RFID tag 300 in the vertical direction is identified,position P₀ in the vertical direction is identified.

Hence, the location detection section 232 calculates (detects) the tagdistance Do (step S115) on the basis of the position P₀ that isidentified. Here, if the position P₀ in the horizontal direction hasbeen identified in step S114, the location detection section 232calculates the tag distance D₀ in the horizontal direction, and if theposition P₀ in the vertical direction has been identified in step S114,the location detection section 232 calculates the tag distance D₀ in thevertical direction. In the case of the method of FIG. 2, the locationdetection section 232 calculates the tag distance D₀ by Equation 5, andin the case of the method of FIG. 4, the location detection section 232calculates the tag distance D₀ by Equation 9. If the tag distance is tobe calculated by Equation 5 in accordance with the method of FIG. 2, instep S115 the parameter acquisition section 231 acquires the distance bin accordance with the mode described above. The location detectionsection 232 uses the acquired distance b to calculate the tag distanceD₀ with Equation 5. Alternatively, if the tag distance is to becalculated by Equation 9 in accordance with the method of FIG. 4, instep S115 the parameter acquisition section 231 acquires the radius rand central angle θ in accordance with the mode described above. Thelocation detection section 232 uses the acquired radius r and centralangle θ to calculate the tag distance D₀ with Equation 9.

Next, in accordance with the tag bearing identified in step S114 and thedistance calculated in step S115, the output section 233 displays thetag object and displays the tag distance in the distance indication areaAR2 (step S116). If this is the first detection of the tag position instep S116 since the start of detection, the display of the tag objectOBJ2 or tag object OBJ12 corresponding to the bearing identificationpoint identified in step S113 is started in the tag location indicationimage (the horizontal direction tag location indication image Gh or thevertical direction tag location indication image Gv) corresponding to aplane direction (the horizontal direction or the vertical direction),and the display of a numerical value representing distance is started inthe distance indication area AR2.

Alternatively, if this is the second or subsequent detection of the tagposition in step S116 since the start of detection, the display of thetag object corresponding to the bearing identification point identifiedin step S113 is updated in the tag location indication imagecorresponding to the plane direction (the horizontal direction or thevertical direction). The tag object is updated in accordance with thetag bearing identified in step S114 and the distance calculated in stepS115.

The tag distance that is calculated in step S115 the first time sincethe start of the detection of the tag location is found incorrespondence with only one plane direction of the horizontal directionand the vertical direction. Thereafter, the tag distance correspondingto the other plane direction is calculated by the loop processing ofsteps S104 to S117 being repeated. Because the tag distance that hasbeen calculated at this stage is calculated using the distance D₁ alongthe tag bearing that has already been determined in correspondence withthe one plane direction, the tag distance has high accuracy with respectto the actual location of the RFID tag 300. Therefore, when the outputsection 234 displays the tag distance found in correspondence with onlyone plane direction in the distance indication area AR2 for the firsttime after the start of location detection, an indication may bedisposed at the distance indication area AR2 to indicate that theaccuracy of the displayed distance may be lower than the accuracy of thetag distance that is to be calculated in correspondence with both theplane directions.

After the processing of step S116, or if it is determined that nobearing identification point has been reached (“NO” in step S113), thelocation detection section 232 makes a determination as to whether thetag location detection has been completed (step S117). If it isdetermined that the tag location detection has not been completed (“NO”in step S117), the processing returns to step S104. On the other hand,if it is determined that the tag location detection has been completed(“YES” in step S117), for example, due to an operation commanding theend of tag location detection being performed or suchlike, the locationdetection processing is ended.

Incidentally, if the tag distance D₀ is calculated by the method of FIG.2, the mode of acquiring the distance b is not limited by the exampledescribed above. For example, the tag reader 100 may be moved by anautomatic guided vehicle (AGV) that is equipped with an encoder and thedistance b may be calculated on the basis of detection outputs of theencoder. As a further example, the portable terminal device 200 mayinput images captured in an imaging direction that matches the antennadirection. The portable terminal device 200 may then carry out imageprocessing to calculate a movement amount from changes in the inputtedimages associated with movements of the tag reader 100 and acquire thecalculated movement amount as the distance b. A configuration is alsopossible in which the tag reader 100 is provided with two of the antenna101, which are separated by a distance b that has been set as a fixedvalue in advance, and the tag distance D₀ is calculated using phases ofsignals received by each of the two antennas 101. In this case too, thedistance b may be stored in the portable terminal device 200 as a fixedvalue.

FIG. 1 shows structures of a tag location detection system according toa mode in which the portable terminal device 200 is fixed to the tagreader 100 by the adapter ADP. However, a configuration is possible inwhich the functions of the portable terminal device 200 are added to thetag reader 100 and the portable terminal device 200 is integrated withthe tag reader 100.

In the descriptions above, the tag location is detected for each of thehorizontal direction and the vertical direction. However, aconfiguration is possible in which the tag location is detected in oneor other of the horizontal direction and the vertical direction. Even ifthe tag location is detected for only one plane direction, the taglocation may be detected using a single frequency with high accuracy,compared to, for example, a case in which plural signals with differentfrequencies are employed as in Patent Document 2. In the descriptionsabove, the distance to the RFID tag 300 and the bearing of the RFID tag300 are detected to serve as the tag location. However, a configurationis possible in which the distance to the RFID tag 300 is detected as thetag location and the bearing of the RFID tag 300 is not detected.Conversely, a configuration is possible in which the bearing of the RFIDtag 300 is detected as the tag location and the distance to the RFID tag300 is not detected.

In the descriptions above, the tag location is displayed at the displayunit 205. However, a configuration is possible in which informationrelating to the location of the RFID tag 300, such as whether a movementis toward or away from the RFID tag 300 and the like, is reported to auser by sounds or the like.

A configuration is possible in which the tag reader 100 is incorporatedin an autonomous device such as a drone or the like and the location ofthe RFID tag 300 is identified on the basis of phases detected by thetag reader 100 while the autonomous device is moving. In this case, thetag reader 100 may have, for example, a shape that is suitable forincorporation in the autonomous device; a configuration is possible inwhich, for example, sections corresponding to the antenna and the readerare physically separated.

An example is given in the above descriptions in which the antenna 101is moved. However, even if the antenna 101 is fixed at a predeterminedlocation and the RFID tag 300 is moved by a conveyor belt or the like,the location of the RFID tag 300 may be identified by a method similarto the methods described above.

An example is given in the above descriptions in which the location ofthe single RFID tag 300 is detected. However, using a similar method tothe method described above, the locations of a plural number of the RFIDtag 300 in a three-dimensional space may be identified simultaneously orsuccessively, and the identified locations of the plural RFID tags 300may be displayed on a map of the three-dimensional space as illustrated.

The tag reader 100, portable terminal device 200 and the like accordingto the embodiment described above may be realized by a computer. In thiscase, a program for realizing the functions of the embodiment may berecorded in a computer-readable recording medium; the program recordedin the recording medium may be read into a computer system and executedto realize the functions. The term “computer system” used herein isintended to include an operating system, hardware such as peripheraldevices and so forth. The term “computer-readable recording medium” usedherein is intended to include a portable medium such as a flexible disc,a magneto-optical disc, a ROM, a CD-ROM or the like, and to include arecording device such as a hard disc incorporated in the computer systemor the like. The term “computer-readable recording medium” is alsointended to include a medium that dynamically stores the program for ashort duration, such as communication lines along which the program istransmitted through a network such as the Internet or the like or acommunications circuit such as a telephony circuit or the like, and, insuch cases, a medium in which the program is stored for some time, suchas volatile memory at a computer that is a server or a client. Theabove-mentioned program may be a program for realizing a subset of thefunctions described above. The functions described above may be realizedby a combination with a program that is already recorded in a computersystem, and the functions may be realized using a programmable logicdevice such as a field programmable gate array (FPGA) or the like.

EXPLANATION OF REFERENCE NUMERALS

-   -   100 tag reader    -   101 antenna    -   102 tag-compatible communications unit    -   103 phase detection unit    -   104 portable terminal device-compatible communications unit    -   111 grip portion    -   200 portable terminal device    -   201 tag reader-compatible communications unit    -   202 sensor unit    -   203 control unit    -   204 memory unit    -   205 display unit    -   206 operation unit    -   231 parameter acquisition section    -   232 location detection section    -   233 output section    -   234 output section    -   300 RFID tag

1. A storage medium location detection system comprising: a storagemedium-compatible communications unit that communicates with a storagemedium by wireless using electromagnetic waves at a predeterminedfrequency; a phase detection unit that detects phases of signalsreceived from the storage medium; a parameter acquisition section thatacquires a distance detection parameter to be used in detecting astorage medium distance from a first position of an antenna to thestorage medium, the first position being a position in a range ofpositions of the antenna from which the distance to the storage mediumis shortest, the distance detection parameter being a predeterminedvalue set in accordance with a positional relationship between the firstposition and a second position, and the second position being a positionof the antenna in the range of positions of the antenna that isdifferent from the first position; and a location detection section thatdetects the storage medium distance, the location detection sectionusing a first phase detected by the phase detection unit at the firstposition, a second phase detected by the phase detection unit at thesecond position, and the distance detection parameter acquired by theparameter acquisition section, wherein the location detection sectionidentifies the first position at a time at which a trend of changes ofphase detected by the phase detection unit in association with movementof the antenna reverses.
 2. The storage medium location detection systemaccording to claim 1, wherein if a right-angled triangle is formed withvertices at the location of the storage medium, the first position andthe second position, the angle that corresponds to the first positionbeing the right angle, the parameter acquisition section acquires thedistance between the first position and the second position.
 3. Thestorage medium location detection system according to claim 1, whereinthe first position and second position are disposed on the same line ofcircumference, and the distance detection parameter that the parameteracquisition section acquires includes the radius of the circumferenceand a central angle of an arc of the circumference whose two ends arethe first position and the second position.
 4. The storage mediumlocation detection system according to claim 1, wherein the locationdetection section detects a storage medium bearing measured from thefirst position on which the storage medium is disposed, the storagemedium bearing being a direction of the antenna that is detected at thetime at which the first position is identified.
 5. The storage mediumlocation detection system according to claim 4, wherein the locationdetection section detects a storage medium bearing and storage mediumdistance corresponding to a horizontal direction, and the locationdetection section detects a storage medium bearing and storage mediumdistance corresponding to a vertical direction.
 6. The storage mediumlocation detection system according to claim 4, further comprising anoutput section that outputs by display the storage medium distance andstorage medium bearing detected by the location detection unit.
 7. Thestorage medium location detection system according to claim 6, whereinthe output section outputs by display the storage medium bearing andstorage medium distance corresponding to the horizontal direction andthe storage medium bearing and storage medium distance corresponding tothe vertical direction that are detected by the location detection unit.8. A non-transitory computer readable medium recording a programexecutable by a computer that causes the computer to realize functionsof: a parameter acquisition section that acquires a distance detectionparameter to be used in detecting a storage medium distance from a firstposition of an antenna to a storage medium, the antenna communicatingwith the storage medium by wireless using electromagnetic waves at apredetermined frequency, the first position being a position in a rangeof positions of the antenna from which the distance to the storagemedium is shortest, the distance detection parameter being apredetermined value set in accordance with a positional relationshipbetween the first position and a second position, and the secondposition being a position of the antenna in the range of positions ofthe antenna that is different from the first position; and a locationdetection section that acquires information representing phases ofsignals received from the storage medium, the first position beingidentified at a time at which a trend of changes of the detected phasesin association with movement of the antenna reverses, and the locationdetection section detecting the storage medium distance using a firstphase detected at the first position, a second phase detected at thesecond position, and the distance detection parameter acquired by theparameter acquisition section.